Interlaminar lumbar instrumented fusion (ILIF™) is a compound surgical solution to spinal stenosis, combining direct neural decompression with an allograft interspinous spacer (ExtenSure® H2) to maintain the segmental distraction, and a spinous process fixation plate (Affix™) to maintain stability for eventual segmental fusion. Because this compound solution requires only a midline incision rather than the far lateral exposure necessary in posterolateral fusion with pedicle screws, it is less invasive to the patient, and therefore should result in less postoperative pain and disability, broadening the applicability of the procedure to even those advanced in age or with existing comorbidities. Subjects will be followed for 24 months following surgery to determine the changes in ODI scores from preoperative to baseline assessments. This data will be compared to published data on similar procedures.